Electrical hydraulic power unit



6 Sheets-Sheet 1 June 22, 1948. E. A. ROCKWELL ELECTRICAL HYDRAULIC POWER UNIT Filed May 6, 1944 June 22, 1948. E. ROCKWELL 2,443,642

ELECTRICAL HYDRAULIC POWER UNIT Filed May'6, 1944 6 Sheets-Sheet 3 3 WW 0 E g W n c w L w \v w J 5 7 7 f I| LH L f j W W 5%; fi a ,L www m w w J ZZZ/wad c2. Zdzwezz June 22, 1948.

E. A. ROCKWELL ELECTRICAL HYDRAULIC POWER UNIT 6 Sheets-Sheet 5 M y 3 a J Z w M xmwym w 6. 3m 23 a Q g d 0 w. n

June 22, 1-948. ROCKWELL 2,443,642

ELECTRICAL HYDRAULiC POWER UNIT Filed May 6, 194.4 6 Sheets-Sheet 6 EA/4E PRESSURE P. 5. m E Q B APPEax. PRESS. 40 A r wm CH BEA/(EN OCCUES VOLUME CUB/C INCHES.

PRESSURE- V01. UNE CUFVE5.

/4 28 42 56 Law Pzsss. FLU/D vurPur ra EXPANDEE TUBE-5 CUB/C INCHES.

a 5/4 V/NG OF lNPUT VOLUME.

. fizveni oru Edi ward Q. cviwel'lf Patented June 22,1948

UNIT ED STATES PATENT Claims.

The present invention relates to power units generally and particularly to units having application to the operation of air-plane and automotive parts and accessories, was made in solving certain problems' involving airplane brakes, as will appeanit is to be understood that in the broader aspects thereof, the same has general application;

A large number of current airplane designs employ an expander tube type of brake motor and these tubes are frequently used inroups of as many as four on each wheel; It is" found that these expander tubes may require as much as 40-45 cubic inches of pressure fluid displacement for merely taking up the slack and bringing'th'e brakes into contact with the brake drum, especially when th'e'brake-s haveb'ecome worn. However, during this initial displacement, that may be referred to as the engaging stage, the pressure necessary to expand the-tubes and the brake blocks against the drums will not" ordinarily exceed more than about pounds per square inch. On the other hand; to set the brakes the desired maximum amount, which action maybe referred toas the squeezestag-e, there may be required as much as' 280 -300 pounds per square-inch, and

during this time the expander tubes maybe addi ti'onallyexpanded about 4-2-45 cubic incl i'es, consuming a corresponding amount of additional pressurefluid. Intypic'al systems currently in use high. pressure fluid is employed in the first stage. operation in a manner that unnecessarily wastes alarge amount of high pressure fluid in merely? bringing the expander tubes and brake blocks into engaging position Where the brakes are just beginning to'be applied;

These current systems consume a relatively tions, it being impracticable to locate the power plant in close proximity to the work to be" performed, due to weight and space requirements thereofi It isaprincipal object of my invention to provideanimproved power unit a'ndcontrol therefor effective to greatly reduce the volume of high pressure fluid required to be consumed in the operation thereof and hence reduce the weight and space requirements of the system. A more particular obj ect of my invention is the; provision of a self contained unitar-y power assembly or packaged power unit that is powerful, efficient. in

its'consumption of pressure'iiuid, and hence'cf While this invention (c1. 24-4 mm 2 relatively light weighawhich unit may be readily placed-in any desiredlocation in proximity to the work to be performed and which requires only a light weight remote control connection to the operator or pilot for remotely controlling the same, all of the elements being so arranged within the unit that all thrust is taken within the unit an'd'nothrust is: transmitted externally thereof to the supportv on which the same is mounted.

Another specific object is the application of the above arrangement to the operation of brakes on the landing. wheels of an airplane; including the jprovisionof at-povler unit that 'maybe placed in any desired location and attached tothe plane as a unit or as a' single packagedassembly'. An example of such unit is one that is adapted for mountington the'lan'ding gear, strut in' close proximity to the wheel brakes; Such arrangement and location has the advantage that the struc turalelements of the unit provide 'for the quick and'efi'ective transfer of a large volume of relatively low pressureh-ydra'ulic fluid the short distance involved; while only consuming a small volume of relatively high pressure fluid for ac compllshing both the setting or engaging stage and the subsequently required'actu'al brake apply ing or squeeze stage. is the provision in one modification of my invention, of a power unit of the abovetype'providing power release of the brakes for fast actionas distinguished fromthe' usual arrangement wherein a-stiff spring isrelied upon toeffect return movement resultingin a corresponding inefficienoy-of brakeapplication.-

A further object is the provision in a packaged unit of the above type of amodulator valve amanner suchas to conserve the high pressure fluid,'resulting in'a large saving in the total power requirements with'an accompanying reduction in the weight of the complete unit, wherebyit' is made practicable to locate the unit adjacent the-work to be-performed or on'the'device tobe operated'and to effectively and efficiently control the unitfrom'a remote position? Itis still another object toprovide ina unitary: assembly of the above' character, an improved hydraulic control arrangement for transmitting manualpressures from the remotely locatedoperator or pilot and co--pilot controldevicesto the modulating valves.

Still another object is the provision in the present combination: of" an electric motor and reciprocating pump unitof a-- diaphragm seal arrangementefiective toeliminate loss of fluid Another detailed object from the device in all positions thereof accompanying maneuvering of the associated airplane, as well as the movement of the elements to which the power unit may be attached.

Further objects, advantages and uses of my invention will become apparent from a reading of the following specification taken in connection with the accompanying drawings which form a part thereof and wherein:

Fig. 1 is a schematic layout view of a simplified typical system incorporating certain of the broad features of my invention;

Fig. 2 is a schematic layout view of a modified system incorporating certain of the features of my invention;

Fig. 3 is an enlarged elevational view in section showing in more detail the power unit proper of the modification of Fig. 2;

Fig. 4 is a plane View of the unit shown in Fig. 3;

Fig. 5 is a broken away sectional view taken substantially on the line 5-5 of Fig. 3;

Fig. 6 is a broken away axial section view of a third modified form of my invention;

Fig. 7 shows a set of curves based on data taken from the operation of a unit conforming with Fig. 6; and

Fig. 8 shows a pair of curves bringing out a comparison between the data obtained by the operation of the unit of Fig. 6 with and without the staging feature of the present invention.

To facilitate an understanding and comparison of the structures of the several modifications, similar designating numbers and letters will be employed insofar as practicable, differing only in the first number for the purpose of differentiating modifications. For example, the power applying motor of the first modification is designated D, that of the second modification 2D and that of the third modification 3D. The piston of motor D in the modification of Fig. 1 is designated 32a while that of the second modification is designated MM, and that of the third modification 232a.

Referring now to Fig. 1 of the drawings, there is illustrated in simplified, schematic form, one typical system incorporating a preferred embodiment of certain of the broad features of the present invention. This system is composed essentially of a hydraulic pressure fluid generating and storing assembly indicated generally at A, pressure fluid on-modulating valve B, transfer and off modulating valve C, hydraulic pressure fluid power applying motor assembly D, and work performing assembly indicated generally at E.

The present invention, in its more specific aspects, is directed particularly to the construction, the arrangement and to the mode of 00- action of oil-modulating valve, transfer and off modulated valve, and power applying motor assembly, in the several modifications illustrated by way of example and their equivalents, whereby to provide stage operation. In the broader aspects of my invention, it will be understood that other equivalent arrangements may be provided coming within the scope hereof. In other words, there is provided, by way of example in Fig. 1, one arrangement for effecting a first or engaging stage of movement of motor D at a relatively low power and low rate of consumption of pressure fluid and a second or squeeze stage at a higher intensified power and relatively higher rate of pressure fluid consumption. The first stage is effective to take up slack and perform any desired portion of the work up to a selected .medi'ate the terminals thereof.

level of power application whereupon the second stage is cut in automatically in a novel manner which eifects a smooth imperceptible transition for accomplishing the final portion of the work. Since the extent of travel during second stage operation is usually relatively small the additional consumption of high pressure fluid during this stage operation is relatively small.

Hydraulic pressure fluid generating and main taining assembly A, may include a pressure generator I0 delivering pressure from a sump tank H through a conventional unloading valve 12 to a pressure accumulator [3. Pressure generator It may be driven continuously as when connected to the power output shaft of an internal combustion engine (not shown) or driven by an electric motor (not shown) continuously or interruptedly. Loading and unloading valve 12 may take the form of any of the Well known readily available constructions effective to maintain hydraulic pressure fluid in accumulator 13 between selected maximum and minimum levels of pressure. Pressure accumulator I3 may take any well known form, including for example, a pair of hemispherical sections Kid and I32), the interior of which is divided by a diaphragm [30 into a hydraulic pressure chamber andan air chamber.

On-modulating valve B may take any well known form, but is preferably of the type disclosed in Rockwell Patent 2,276,418 and includes essentially a housing I 5 enclosing balanced highpressure inlet valve l6, cooperating with seat Ilia and having a relief or return valve portion I62), valve It being normally urged into engagement with seat 15a by a compression spring I60. A reciprocable tubular sleeve i1 is formed at one terminal with a valve seat for valve lfib, and with radial low pressure return ports IIb inter- A compression spring I'la normally urges reciprocal tubular valve element ll in the direction out of engagement with valve 16b and a manually engageable pedal I8 is operable through levers Mia and link 18b to move tubular valve element ll into engagement with valve Ifib against the action of spring Ila to effect openin of on-modulating valve proper It and the modulated introduction of high pressure fluid from the accumulator past valve seat [6a to motor assembly D and transfer and off modulating valve assembly C. Relaxation of the pressure on manual pedal it results in spring Ila moving valve sleeve I! out of contact with conical valve Nib, permitting inlet valve I6 to close against seat Ito and allowing the fluid to be discharged from the motor assembly D through the interior of tubular valve element I1 and. radial port llb thereof back to sump ll.

Transfer and off modulating valve assembly C is, in some respects, similar in construction to on-modulating valve B, certain parts being reversed as will appear. Housing 25 contains a reciprocable transfer valve 26 engageable with a seat 2611 at the end of the fluted terminal of a tubular off modulatin valve stem 21, but normally held open by a compression spring 21a. Tubular valve stem 21 is formed on the periphery thereof with an off modulating valve 21b, engageable with a complementary seat carried by the housing and is normally urged into engaged position by a compression spring 210. It is important to note that since the transfer valve 26 is normally urged into open position by compression spring 21a pressure fluid is directed therethrough to surface Y during the first stage operation as will. app r-u r the purp se: f, m vin a ve: as into: en agement. with. seat: 28a? aga n t he action of? spring; En land effecting the 9 112; of off. modulatin alve. 1 t e e: siprovid d a: flu d pr ssure responsive mot-or: 28 inc uding. a piston 25a.- anda; connecting link 23!}. passing through a partition inI thev housing; 25 andv driV- in ly engaging. valve-26, theemotor 28 being sup plied with operating fluid. pressure, through a, special control lineras will appear.

Hydraulic pressure fluid-- power applying motor, assembly. D; comprises essentially.- a, housing 30. formed; with, a. cylinder 3J1 receiving; a. reciprocable piston andplunger assembly 32 including pistontEa. receiving modulated. pressurefrom on modulating. valve 3 in contact with the-upper majcn working, surface X, thereof and the same pressure, directed through transfer and off modue lating valve C toa small opposed differential working surface Y during initial pressure fluid application, with transferand. off modulating valve, C in. open positionas, shown, during. the first stage of operation that be referred to as the engaging stage Thisrelatively smaller difier ential, area. Y is. defined inv part by. plunger 32b which-passes. through-an orifice 301av inv the housing 3,0. Compression spring 320 is effective to return piston, assembly 32, to the off position thereof; upon: the: release of, pressure. fluid from, contact with piston 32a. 'll'he necessary sealing ringsare employed, as. indicated to prevent leakage of. they fluid past the piston and plunger.

It. willappear. that by virtue-of thediiferential in area between opposed surfaces X and Y, the delivery. of the same pressure tov both surfaces will be effective-to move the power applying piston assembly 32 and thereby deliver a; first relatively low, level of. powerfor the first or engaging stage.

Particular attention is drawn tothefact that as piston.32a. is moved outwardly, pressure fluid. inv contactwith the smaller differential area Y, is transferredbackthrough transfer and off. modua latingvalve C and.th ence into contactwith op-, posed larger: differential, area X of piston 32a. This is made-possible by the fact that valve 26 is heldppen by spring 21a during the first stage operation; Thus it will be seen that a major economy in the consumption of high pressure fluid is accomplished during the first stage of operation by transferring the, pressure fluid in contact; with relatively smaller difierential, area through the transfer oif, modulating valve C to-major working surface X-of piston 32a. Therefore only just sufficient high pressure fluid from accumulator 6-3; is required to be consumed to. displace avolume equalto the diiierence in the areas of surfaces X and Y multipliedby the-distance of: travel of the piston during the engaging stage. This is; a relatively. small volume of high pressure fluid and a considerable saving of high pressure fluid is thus realized.

The valueof theclifferential between the areas X, and Y, may be varied to, suit the particular installation.

For the purpose of amplifying. the power output of motor piston assembly 32. the pressure fluid in. contact with the relatively small differential area Y is shut ofi from communication with the Orr-modulating valve pressure and placed: incommunication with the sump: tank; H- by the automatic operation, of. transfer andv oif modulating, valve (3, upon. the;- occurrence of av selected delivery pressure I to; major working sure face, X. To.this--end;a pressure control 11116133.;

' B, providing an intensified application of pres the, lightof: the present disclosure.

places; the; modulateddelivery pressure; fluid.

which is in contact with differential areaX of.

piston, 32a, also in communicationwithipressure fluid; responsive motor 28a of: transferand off modulating valve Ch Thereforawhen the pressurefiuid modulated tosurface-X of piston 32a,

rises to aiselected value as determined-by the adjustment of spring-21a of transfer andfoff modulating valve C, then valve motor piston 28a becomes eifeotiveto shift valve-26 intocontact with seat 2 61; shutting off communication of fluidpressure from. on-modulator valve B, andv stopping deliver-y thereof to difierential surfaceY. Still further movement, of transfer valve 25 becoming effective to open off modulating Valve.

27b off modulating pressure fluid; from; contact with smaller differential surface Y and returning the same to the sump tank I i, thusrendering the complete area of surface X effective in response to pressure deliveredfrom on--modulating valve sure'to piston. assembly. 32-for afinal or squeeze stage of operation.

Forthe purpose of illustrating-the general api plication of the present multi-stage operation comprising my invention, the work performing assembly'E isshown as comprising an; anvil 40 receiving a distortable workpiece H engageable by a die member 42 carried by the lower terminal.

of power plunger 32b. The first stage of operation may bring the die 42 into contact with the work piece 4!, distortthe same into substantially flat engagement with the anvil wand if desired, perform a certain portion of the complete distorting or shaping operation, this being followed,

fluidin, contact, with; the lesser surface being transferred toithe greater surface during the first or, engagingstageof operation to thus conserve the total amount of f' pressure fluidcon sumed, t-hisfirst stage operation .beingfollowed by, shutting; off: of communication of the pressure source with the smaller surface andv off modulating of the: pressure from-the smaller surface to, the low pressure return tothusrender the major; surface: moreeffective and provide an amplified'power application or squeeze state.

This broader aspect of the present invention should not be limited to the specific arrangement of values-orothermeans provided foreffecting theabove described delivery of pressure fluid to and removal fromthe differential surfaces, as other modifications may suggest themselves in of broad'importance .isthe circulating. or deliver-- ing. baclgof the operating. pressure fluid from. the a leading surface. Y.,to..the trailing surface X dur ingthe firststagethuseifecting a major economy followed.- by. offdelivery from the leading surface, Y to:a low: pressure 20.1 6 duringthesecond-stage. For; example, the operating: liquid, were man a ly:- eenerated: by a. master cylinder. in.-

stead: of; m dulated; from: an? accumulator. then...

The thing this economy or advantage might take the form of reduced pedal travel.

Particular importance is directed to the smooth imperceptible transition from the engaging stage of power application to the squeeze stage of power application. This improvement is directly attributable to the off modulating of pressure fluid from the smaller surface Y. This is to be clearly differentiated from the producing of a transition by introducing pressure fluid successively into contact with additional surface areas acting in the same direction. This latter arrangement invariably produces bumpy or clearly detectable rough operation upon transition between stages.

Turning now to an alternative modification, there is shown in Figs. 2 through 5 a power unit arrangement suitable for incorporation on an aircraft where the reduction of over-all weight and maintenance of high eificiency is a major problem. By employing my novel high-pressure fluid conserving arrangement, it has been made possible to so reduce the over-all weight of a complete power unit and large volume low pres sure generator that the complete unit may be mounted on the oleo or landing strut of an airplane and function to quickly deliver low pressure, large volume pressure fluid for the operation of the expander tube brake on the associated landing wheel.

In this modification, hydraulic fluid pressure generating and maintaining assembly 2A comprises a reciprocating plunger generator pump H0 delivering to an accumulator H3 in which arange of pressures is maintained between selected maximum and minimum values by means of a pressure responsive switch assembly H2, efiective to cut the driving electric motor on and off depending upon the level of pressure. A piston H30 divides accumulator H3 into an upper hydraulic pressure fluid chamber and a lower air pressure chamber, the accumulator being in the form of a cylinder providing for the shifting of piston H30 with changes in pressure on the opposite sides thereof.

Pressure fluid generator assembly H0 comprises essentially a reciprocable plunger IIIla. operable in cylinder IIIJb receiving low pressure fluid through swiveled pickup tube Hllc and discharging pressure fluid through check valve I Iild into the upper portion of accumulator H3. The pump housing IlUe enclosably supports an elec tric motor IIIlf driving an eccentric Hlly, oper ating a reciprocating connecting rod Huh, drivingly associated with the pump plunger mm through a diaphragm I I 07. This diaphragm is sealably associated with the housing about the periphery thereof and performs the important function of preventing the fluid from leaking therepast irrespective of the angular position of the equipment due either to movement of the supporting strut or the manipulation of the plane.

On modulating valv 23 and transfer and off modulating valve 20 are formed as a unit and ated master cylinder II8a operated by the pilot through treadle I I8 and effective to transmit control pressure through conduit 8b. Duplicate treadle controls are shown for the pilot and copilot, double check valv H being effective to prevent operation by one master cylinder when the other has already been operated. Piston I28a of transfer and off modulating valve operating motor I28, instead of being made responsive to the pressure delivered to the power applying motor 2D, as in the modification of Fig. 1, is made responsive to the control pressure delivered from the pilots control treadle H8. This motive piston I28a is placed in communication with the motive piston I I'Ic through passage I29 in off modulating valve housing I25. Pressure fluid is delivered from the accumulator to oil-modulating valve H6 and also by means of a passage I29a, is delivered to transfer and off modulating valve 20. Valve I26 of transfer and off modulating valve assembly 20, being in open position full accumulator pressure is delivered to the smaller differential area 2Y of pressure fluid power applying motor 2D and this functions to produce pressure return of the motor to off position thus making possible the elimination of a return spring. This is distinguishable from the arrangement of the modification shown in Fig. 1, wherein the motor is returned to off position by means of coil compression spring 320.

Hydraulic pressure power applying motor arrangement 2D is similar to that of motor D in the modification of Fig. 1 except as will be pointed out. Piston and plunger assembly I32 comprises a separable piston I32a threadabl secured to the upper terminal of tubular plunger I32b. Depending from housing I30, is a fixed travel coordinating monitor plunger I301), sealably and telescopingly receiving motor plunger I32!) and piston I32a for reciprocation thereon. Motor plunger I321) passes through an orifice I300, in orifice closure plug I380. This closure plug is externally threaded for reception within the lower terminal of cylinder I3I. The lower terminal of motor plunger I322) is closed by a threaded plug I32d. The interior of monitor plunger I301; is placed in communication with the pilot master cylinder H811. through conduits H82) and. NM. The pressure exerted by the pilot through treadle H8 and master cylinder II8a is transmitted through monitor plunger I30b to the closed terminal of motor plunger I32b acting on surface Z of closure plug I32cl. Therefore, the effort exerted by the pilot on treadle I I8 is transmitted in the form of work to surface Z and the pilot thus performs a definite though small proportion of the work in moving the motive piston and plunger and this gives the pilot the desired reaction simulating actual manual brake application. In addition, as power applying piston I32a moves with reference to the monitor plunger I32b, the effect thereof evidences itself to the pilot by a corresponding travel of treadle H8. Thus the pilot experiences a pedal feel and travel which is the same as if he were actually applying the brake with his foot.

The work applying or power consuming assembly 2E, in this modification, is a low-pressure relatively largevolume pressure fluid generating cylinder I40, having the function of supplying presure fluid through a short conduit link I IIa to the expander tubes I41 of an airplane wheel brake, the drum of which is indicated schematically at I44. It will be noted that this type of airplane brake requires a relatively large volume of pressure fluid at a relatively low pressure, it being important that the fluid 'be delivered thereto quickly as well as relieved therefrom quickly. In currently employed arrangements wherein the low pressure'fluid generator must necessarily be located at a considerable distance away from the expander tube, it is very difficult, if not impracticable to obtain this rapid delivery and release cf relatively low-pressure, large volume of fluid. Due to the excessive over-all Weight of currently employed systems, the same are not capable of being mounted in close proximity to the Wheel brake. 'On the other hand, by virtue of the economy and 'efiiciency realized by my system, it is madepracticable to mount the entire unit as .a package or unitary assembly on the strut "or oleo adjacent the wheel brake. The housing I30 is provided with a plurality of attac'hing bosses [38d adapted to be connected with the landing strut 139a through the medium of embracing straps Ittf or their equivalent.

The low-pressure large volume cylinder 'I to receives piston M2 "therein for reciprocation by power applying motor 2D. Piston I i-2 is drivingly connected with the terminal of plunger 132'?) through a lost motion and makeup valve assembly hi3. Piston M2 is formed with acentral bore Mia through which extends "a. fiu'ted portion I32ecf plug 13212. A valve I43a is "carried by plunger I32?) for cooperation with seat 1431). Stop shoulder 'I'3c'g defines the off position of piston IE2. The central portion of housing 139 between motor 2D and low pressure generating piston M2 provides a sump or low pressure reservoir ISM in communication at all times with the makeup valve M3. Star spring I430 is "so arranged that it absorbs any light shock -between closure connecting plug I32d and piston 1'42 upon relative movement in the opening direction. 'It willappear that makeup valve Hi3 willbe opened by relative movement between piston I42 and power plunger I321) at any time and at any position of piston M2 when the driving force from power applying piston [32a is relaxed, the makeup of fluid thus notbeihg limited to the complete ofi position of piston M2 in contact with stop shoulder 130g.

The specific arrangement of pressure responsive switch assembly [i2 does not form part of the claimed subject matter of the present invention, the same being covered 'by Holt, U. S. Patent 2,405,142. For the purpose of understanding the present invention, switch assembly I 52 includes pressure responsive diaphragm I We, pressure transmitting plunger H21), switch body H20 pivotally supported at i IZd, snap acting, switch contact supporting spring H'Zecontactedby plunger H21), and telescoping threaded adjusting assembly H21. Adjusting assembly H2 includes 'a spring operated plunger H29! contacting the underside of switch body Il2c. This arrangement makes it possible to maintain a relatively small differential of pressure between selected levels while at the same time e'fiecting positive and unfalterin'g operation of the control switch for electric motor H81.

For an understanding of the operation of the arrangement of Figs. '2 to reference is now made particularly to the schematic layout of Fig. 2. Operation of treadle M8 by the pilot causes master cylinder Mild to transmit a corresponding pressure to piston Mic of on-modulating valve 2B to piston 8528a of transfer and off modulating valve and to monitor plunger assembly I381) for acting on Work sharing reaction surfaceZ. In the position -:of the elements shown, high pressure fluid from accumulator H3 stands in communication with the smaller one of the differential areas QY of motor 2D, the same having moved the motor to the complete ofi position. No pressure fluid is acting on the major or larger differential area 2X of the motor '21). As soon as the pilot has transmitted a suflicient level of control pressure to piston H10, then the same becomes effective to modulate pressure through onmodulating valve 20 to the upper major differential area *ZX'o'f motor'2D. This is accomplished by the shifting of tubular'valve element 'I it into contact with return Valve portion 1163b of onmodulating valve H6 to thus shut 'oif communication with the low pressure return and subsequently 'open on modulating valve proper lit to an extent determined by the pressure applied by the pilot to treadle :I It. This modulated pressure transmitted past valve seat 1 Ida is delivered to the upper :or major differential area EX of the motor 213. When the level of the pressure delivered to surface 52X has been raised to a surficient'valu'e to overcomethe full accumulator pressure acting on -the opposed smaller area 2Y, then the motor plunger I322; starts moving outwardly. Attention is again directed to the fact that as leading surface 2Y displaces the high pressure fluid in contact therewith, this pressure fluid instead of being spilled'into the low pressure return as in the case of currently available systems, is instead transferred back through open transfer valve I26, communicating passage 12%, ole-modulating valve housing I I5 about valve I in and to the opposed major differential area 2X making up a considerable portion of the pressure fluid required to be delivered to area 2X. in other words, the transfer of pressure fluid from leading sur face 2Y'to trailing surface 2X reduces by a sizable amount the total volume of high pressure fluid from the accumulator consumed during the initial or first stage operation of motor 2D.

Movement of power plunger I321) first becomes eifec'tive to take up the slack in makeup valve M3 closing the same and driving the piston it? of the low-pressure large-volume generator 2E, thus delivering a first level of operating pressure through relatively short conduit I Ha to the expander tubes M1 efiecting slack takeup and brake engagement, this being referred to as the brake engaging stage.

With the slack taken up and the shoes in engagement with the drum 144, the 'treadle M8 offers additional opposition to movement by the pilot's foot and the application of further pressure by the pilot becomes effective on plunger I-Zlia of transfer and off modulating valve EC to move transfer valve 1'26 against the action of compression spring 127a, effecting the closing of transfer valve 126 and the shutting off of communication between the accumulator and leading surface 2Y-of motor 2D. Further movement of piston "l2'8a becomes effective to shift tubular valve element I2 and gradually open off modulat-mg valve P211), in proportion to the pressure 'exert'ed'by the pilot on treadl'e 'I it. The opening of off modulating valve I 21b is efiective to on modulate the fluid pressure from-communication with leading surface LZY and spill or discharge the same into the low pressure return reservoir 'I3'0h. By the exertion of sufficient additional pressure on'treadle 'l I8,the pilot can effect complete opening of off modulating valve "I 2'Tb, completly relieving leading surface ZY from the action of pressure, thus rendering the entire surface 2X effective in response to the maximum pressure delivered thereto through on-modulating valve HE, and effecting the maximum application of fluid power to motor 2D and the consequent generation of maximum pressure by piston I42 delivering to the expander tubes it! of the brake.

It will further appear that the pilot will maintain a feel or reaction indicating to him the extent to which the brakes are being applied. In other words, the pilot will feel the reaction on both valve operating plungers H and l28a. In addition, the pilot does an amount of work which bears a definite ratio to the total work involved since the pressure from the master cylinder I l8a is delivered through the monitor plunger I32?) to surface Z, the travelling of this surface Z also giving the pilot the desired pedal travel.

While I have described only one unit by way of example, it will be understood that a similar unit is contemplated for installation on each of the two principal forward landing Wheel struts.

Turning now to still another modified system incorporating my invention, reference is had to Figs. 6 to 8. Referring first particularly to Fig. 6 showing schematically the essential portions of the layout, incorporating this modification, particular emphasis will be placed in the description on the features of difierence. Instead of rendering the off modulating valve responsive to a selected level of accumulator pressure delivered to the primary motor surface as in the modification of Fig. 1, it will be noted that pressure responsive piston 228a, of motor 228 forming part of transfer and off modulating valve 30, is rendered operable in response to the generation of a selected level of low pressure fluid in cylinder 24!] of pressure generator 3E. Coil compression spring 2320 functions to return motor piston 232a to off position as in the modification shown in Fig. 1, instead of returning the same by pressure as in the modification of Fig. 2.

Any suitable pressure generating and maintaining arrangement may be employed, such for example, as that shown in the modification of Fig. 2 or preferably an arrangement of the type disclosed in Rockwell Patent 2,197,772. Any desired on-modulating valve arrangement may be employed such, for example, as that disclosed in connection with the modifications of Figs. 1 and 2 or preferably that disclosed in Rockwell Patent 2,244,966, which is effective to give the optimum mode of modulated pressure delivery irrespective of the pressure level at which operation is desired, as Well as being effective to give other desirable characteristics.

Referring in greater detail to Fig. 6, there is illustrated a motor 3D and low pressure large Volume generator 3E, in a form particularly adapted for production including the transfer and off modulating valve 30, the pressure fluid power applying motor 3D, the low pressure large volume generator 3E, and the low pressure return sump and makeup reservoir 23th, all in one unitary assembly, particularly adapted for installation on an airplane in a similar manner to that disclosed in connection with the modification of Figs. 2 to 5.

Transfer and off modulating valve assembly 30 is similar to the corresponding valve assembly in the previously described modifications, except as will be pointed out. Valve housing proper 225 is preferably formed as an integral part of motor housing 230 and is positioned in opposed relation to the lower terminal of motor cylinder 23L The inlet pressure from the pilot treadle master cylinder operated on-modulating valve (not shown) is directed through conduits 226b, tubular valve member 221, and passage 225a into the lower portion of motor cylinder 23! into con-- tact with the smaller one of the differential piston areas 3Y, when the pilot operates the treadle. Spill passage 226d directs 01f modulated pressure from contact with surface 3Y through passage 2260 and off modulating valve proper 2211) in response todevelopment or generation of a se-- lected valve of pressure within low pressure generator cylinder 249. Generation within cylinder 24!] of the selected value of low pressure acts through control line 233 and off modulating valve motive piston 228a to effect the closing of transfer valve proper 226 and the opening of off mod-- ulating valve proper 22711 to off modulate the pressure from contact with relatively small surface 3Yand thus render more efiective the relatively large surface 3X. Spill passage 226d discharges into the sump or makeup reservoir 23077. from which the low pressure fluid is subsequently picked up by conduits zlllc and directed back to the fluid pressure generator inlet (not shown).

The power applying motor assembly 3D is generally similar to that of the modification of Figs. 2 through 4, except as will be pointed out. Motive piston assembly 232 includes a separable piston 232a and a plunger 232b having the inner end thereof closed,,this piston portion being fastened in installed position by a snap ring and the necessary sealing rings employed to provide a seal, as indicated. 1 An air bleed valve assembly 232 is formed in the terminal of plunger 7232b for the purpose of effectively ejecting any air that may have accumulated in the unit. This valve assembly includes a valve proper 232g for controlling communication between the two faces of piston 232a, this valve being normally urged in the direction of closed position by compression spring 23%. Spider member 2327' is mounted in the upper portion of cylinder 23! and is effective when piston 232a is moved into the retracted position thereof to open valve 232g against its operating spring 2327i. Compression spring 2320 functions to return the motor assembly to off or retracted position upon the release of pressure from acting on motive piston 232a,

Low pressure, large volume generating piston 242 is generally similar to that of the modification of Figs. 2 through 5, except as will be pointed out. Instead of a fluted closure plug in the lower terminal of plunger 232b, this modification includes the return sprin 2320 passing up through the lower portion of plunger 232D engaging the closed terminal portion thereof, this spring being spaced from the plunger by perforated sleeve 243d allowing the free passage through radial ports 232:: of the necessary makeup fluid pressure required in cylinder 22%. Conical shaped valve 24311 is formed on the outer periphery of plunger 232?) above radial ports 2326 and cooperates with a seat 25,3?) and piston 212 to control the flow of fluid through radial passages 232a It will thus appear that this modification differs principally from so-called de-booster valve cylinders in current use by the incorporation of my high pressure fluid conserving feature wherein transfer and off modulating valve 30 is employed in connection with difierential pressure areas 3X and 3Y to automatically provide twostage operation.

Referring now-to Figs? and 8,-severalcurves 'have been' plotted 'based on actual and calculated data which "curves bring out quite clearly the improvedeffi'cien'cyand importantsaving of high pressure fluid by employing 'my invention.

Referring *first to Fig. 7, brake *pressures have been plotted against volume of pressure fluid consumed in expanding the brake tubes of a commercial --brake expander tube assembly, this data having been taken both when the brakes were new and after thesamehad become considerably worn. It is readily apparent that with this-typeof brake the volume of fluid required rises rapidly as the brake assembly abecomes worn.

Turning now "to Fig. -8, test data was first recorded for the same construction operating in the manner in current practice, with the conserving feature out of operation, namely, leaving outthe operation of transfer andoff modulating valve ECWlllh nodelivery of pressure to surface 3Y. The upper-dotted line-curve shows the 'resultof this operation, high pressure fluid input to the work applying motor cylinder in contact with surface 325 being plotted again-st low pressure fluid output from cylinder 24% to the'expander tubesof-the brake.

Next, data was calculated for an "operation of structure conformin with the 'disclosureof Fig. 6, "fluid pressure being delivered to motive piston surfaces 3X "and -3Y through transfer valve 2% during the first stage "of "operation followed by the automatic operation of off modulating valve 22717 in response to the development of a selected value df pressure in the cylinder 2 eifective to off modulate pressure fluid from surface 3Y to the lowpressure reservoir 23th. The data obtainedds incorporated/into the solid line curve below the above described dotted line curve in Fig. The cross-hatched area between these two icurves'indicates quite clearly a'majorsaving in the total volume of high :pressure i'luid consumed'by'employing my'invention.

While I have described my invention in connection with certain specific embodiments thereof ,it .is .to .be understood that this is byway of example only and that my invention is to be defined by the. appended claims.

I claim:

'1. In combination with an aircraft landing strut which includes a Wheel brake having brake expander tubes adapted to receive a relatively large volumeof'low-pressure fluidthrough a short fluid link; those improvements which include .a packaged power unit comprising means defining a housing attached to the landing strut closely adjacent abrake expander tube, said housingfincorporating .a hydraulic pressure'fiuid power applying ,piston assembly, means defining a low pressure large volume pressure generating piston assembly, means drivingly'conn'e'cting said'power applying piston assembly and said low pressure generating ,piston assembly, means defining a fluid pressure generator, means de'finingan electrictmotor .driving said generator, :means defining a fluid .pressure accumulator receiving pressure from said generator, said power lpistonasserribly including a ,pair of opposed differential pressure responsive surfaces including ,a relatively large major trailing surface and a relatively small leading surface, means fornormallyidelivering pres sure from said accumulator to said leading surface for eiiecting retracting movement of said power applying piston. assembly, :means defining an on-modulating'valve assembly, efiectivewhen operated to deliver modulated pressure to said relatively large trailing differential surface for overcoming the opposing action of accumulator pressure acting on said leading differential surface, :said means "effective "to normally deliver accumulator pressure to said leading surface "comprising a transfer and, on modulating valve assembly, including a transfer valve portion effective when-open to pass accumulator pressure t'o'said leading one of said surfaces and further effective upon initial operation of said power applying piston assembly to transfer pressurefiuid from said leading surface back through said transfer valve to the trailing major one of said differential areaswo thus make up a portion'of the total pressure fluid delivered to-said major surface, means defining a remote manually controllable pressure controlline said On-Il'lO'dlllfilZ- ing valve assembly further including pressure responsive motive means for operating the same, said transfer and off modulating valve assembly further including pressure responsive motive means for operating the'sam'e, both of saidlastnamed motive means being under the control of said manually controllable pressure control line.

-2. In combination with an aircraft landing strut which includes a-wheel brake havingbrake expander tubes adapted to receive a relatively large volume of 'low pressure fluid through a short fluid link; those improvements which include a packaged power unit comprising means defining a housing attached -'to the landing strut in close proximity'to a-brake expandertube, said housing-incorporating a hydraulic pressure fluid power applying piston assembly, a low pressure large volume pressure generating piston assembly, means drivingly'connecting said power applying-piston assemblyand said low pressure generating piston assembly, means defining a low pressure return'fiuid reservoir in communication with said connecting means between said power piston and said generating piston, said connecting-means-further including a lost motion operable low pressure *fluid makeup valve, means de fining a fiuid pressure generator, an electric motor for "driving said-generator, means defining a pressure fluid accumulator receiving pressure fluid from said generator, said power piston assemblyfurther in cluding a pair ofopposeddiiferential pressure responsive surfaces comprising a first *madorsurface trailing in the on direction of 'operation'anda smaller minor surface leading in "the direction of -on operation, means for delivering pressure fluid from said accumulator to said respective surfaces including a first transfer and off modulating valve assembly effective in the normal position thereof to deliver accumulator pressure 'to said minor one of said differential surfaces and-beingffurther effective upon the op eration'of said power piston assembly to transfer pressure fluid from said minor surface to said major surfaceto-thusmake up-a portion of the pressure fluid delivered to said major surface, thus conserving the total p essure fluid consumed, means defining an on-modulating valve assembly,efiective to deliver modulated pressure fluid from said accumulator to saidmajor oneof said surfaces, means defining a remote manually operable-control 'line, said (in-modulating valve assembly comprising pressure responsive motive means for operating the sameyboth of said valve pressure responsive motive means being operable by saidmanua'lly'operable control'line,-said-trans fer and on modulating valve motive means being operabl'ein'respons'ive' to a selec't'edrelatively high pressure in said control line whereby pressure fluid is first delivered to both said major and said minor surfaces for producing a first or engaging stage of operation followed by the operation of said transfer valve to closed position and the further operation thereof to off modulate the pressure fluid from said minor surface to thus pro vide a second or squeeze stage of operation.

3. In combination with an aircraft landing strut which includes a wheel brake having brake expander tubes adapted to receive a relatively large volume of low pressure fluid through a short fluid link; those improvements which include a packaged power unit comprising means defining a housing attached to a landing strut adjacent a brake expander tube, said housing incorporating a hydraulic pressure fluid power applying piston assembly, a low pressure large volume pressure generating piston, means drivingly connecting said power applying piston and low pressure generating piston, an electric motor incorporated within said housing, a fluid pressure generator incorporated within said housing driven by said electric motor, a fluid pressure accumulator incorporated within said housing and receiving pressure from said generator, a low pressure return fluid reservoir incorporated within said housing supplied by said generator, said power piston assembly including a pair of opposed differential pressure responsive surfaces, means for delivering pressure from said accumulator to said surfaces including a modulating valve assembly effective in one position thereof to deliver pressure to both of said areas, the difference in the areas of said surfaces being effective to cause movement of said power piston to drive said pressure transforming piston to generate and deliver a relatively low pressure fluid adapted to operate a brake expander tube for producing the engaging stage, said valve assembly being effective during said engaging stage to cause the transfer of high pressure fluid from the leading one of said power piston surfaces to the trailing one of said surfaces to thus limit the total volume of high pressure fluid consumed during said engaging stage to the product of the difference in said surface areas multiplied by the distance of travel of said power piston, said modulating valve assembly being additionally operable following said engaging stage to cut off communication of said high pressure fluid with said leading power piston surface and effective to off modulate the said fluid pressure from contact with said leading surface back to said reservoir to thus render the pressure in contact with said power piston trailing surface fully effective for applying a greater force to said transforming piston to cause the same to deliver an intensified pressure for accomplishing the squeeze stage of operation, said modulating valve assembl including pressure responsive means for effecting said sequence of operation and manually controlled means for applying said control pressure from a remote position in accordance with the brake application desired, said connecting means between said power piston and said pressure transforming piston passing through said low pressure return reservoir and including valve means responsive to the relative movement of said pistons for placing the leading surface of said transforming piston in communication with said low pressure reservoir for making up any deficiency in the fluid link between said piston and said expander tubes.

4. In combination with an aircraft landing strut which includes a wheel brake having brake expander tubes adapted to receive a relatively large volume of low pressure fluid through a short fluid link; those improvements which include a packaged power unit comprising means defining a housing attached to the landing strut adjacent a brake expander tube, said housing incorporating a hydraulic pressure fluid power applying piston assembly, a low pressure large volume pressure generating piston assembly within said housing, means connecting said power applying piston assembly and said low pressure generating piston assembly and conduit means adapted to connect said low pressure generating piston assembly with an expander tube of an aircraft brake.

5. In a self-contained electric hydraulic power t pted for the operation of brakes, having a connection leading to a remote manually controlled master cylinder, and a hydraulic connection to a hydraulic motor which is adapted for the actuation of brakes, those improvements which comprise a housing means comprising a fluid supply reservoir and an accumulator, a pump located within the housing means having an inlet port leading to the supply reservoir and a check valve between the pump and the accumulator located within the housing means, and a modulator valve assembly including master cylinder pressure responsive plunger means and valve means, adapted to receive fluid from the accumulator for the operation of brakes and to discharg fluid into the supply reservoir upon release of the brakes, and a piston means associated with the output connection to the brakes, having a travelcoordinating device cooperating with a valve operating plunger to effect an increasing pressure with the increased travel thereof and adapted to be connected to the master cylinder by said first manual connection, and a pressure-operated switch on the housing means for controlling the electric motor so as to maintain a substantially uniform level of pressure fluid for the operation of the brakes, the elements herein specified, with the exception of the master cylinder connections and motor, being arranged in a unitary structure for unit handling and assembly.

EDWARD A. ROCKWELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 433,822 Robb Aug, 5, 1890 523,419 Thorpe July 24, 1894 1,846,089 Davis Feb. 23, 1932 2,009,515 Pardee July 30, 1935 2,029,096 Doyle Jan, 28, 1936 2,136,638 Rockwell Nov. 15, 1938 2,142,628 Ballert Jan. 3, 1939 2,163,627 Peterson June 27, 1939 2,296,145 Christensen Sept. 15, 1942 2,322,063 Schnell June 15, 1943 2,328,637 Freeman Sept. 17, 1943 2,329,709 Fischer Sept. 21, 1943 2,345,165 White Mar. 28, 1944 2,352,344 Rockwell June 27, 1944 2,356,366 Wise Aug. 22, 1944 FOREIGN PATENTS Number Country Date 43 Great Britain 1893 447,829 Great Britain May 19, 1936 

